The main annular converter body (2,3) is for the catalytic combustion of a fuel and air mixture and has a through-hole (2b,3b) in the centre. A fuel supply (10,12) is on one side of the main body which has an air inlet (7,8) at one end. A combustion cylinder (4) contains the main converter body. The other end side of the converter body has a pre-mixing chamber (13). Part of the waste gas is circulated by a main nozzle (6). A waste gas mixing cylinder (5) is positioned in the through-hole.
